Estimate the surface are of the figure below using the Trapezoidal Rule.http://i26.tinypic.com/i1b7t1.png
I did:
(40-0)/(2(4))[6+2(5)+2(4)+2(5)+5]
5[39]=195 ft^2
The thing is, apparently the correct answer is 250 ft^2 and I don't know why.

Any help is greatly appreciated :)

Aug 31st 2009, 09:40 PM

Matt Westwood

Can you explain the source of the formula you are using - I'm confused by the 40-0/2(4) bit at the start, and how you got that to equal 5.

Also, I suspect that what you've done is ignored the bits at the ends - but I don't know how you were told to estimate those.

Aug 31st 2009, 09:47 PM

Naples

Quote:

Originally Posted by Matt Westwood

Can you explain the source of the formula you are using - I'm confused by the 40-0/2(4) bit at the start, and how you got that to equal 5.

Also, I suspect that what you've done is ignored the bits at the ends - but I don't know how you were told to estimate those.

Okay, gotcha - I was confused by the dodgy bracketing in the first posting.

So, I suspect what you've done is ignored the bits at the end. Estimate them as trapezoids from 0 to 6 and from 5 to 0 and make them 10 wide, I suppose.

Sep 1st 2009, 06:29 AM

HallsofIvy

Yes. The distance from the left vertical line to the right vertical line is 40 but it looks like the entire region goes from 0 to 60. (The "trapezoids" on the left and right will be triangles. If it were me, instead of using the "trapezoid rule" formula, I would estimate the areas of the four trapezoids and two triangles involved and add them. Doing that I get 250.)

Sep 1st 2009, 08:01 AM

Naples

Thanks for the help guys, I tried it the way HallsofIvy said and also got 250 so I'm going to stick with that.